It is known to print textiles and other materials, particularly synthetic fabrics, by heat transfer dye printing using sublimable or vaporizable dyes which have been imprinted in a pattern or design upon a substrate such as paper. Heat transfer printing has been described in French Pat. No. 1,223,330 and in Swiss Pat. No. 476,893. Such printing techniques, however, are subject to limitations. Thus, it is particularly difficult, and in some cases impossible, to obtain certain complicated patterns or designs involving multicolored combinations of dyes.
In printing heat transfer dyes on a substrate to form a multicolored design to be transferred, differently colored dyes are successively deposited on the substrate. When these successive deposits overlap, stronger, darker prints are formed because, when dye is printed over dye, each dye reinforces the color developed by the other. White is produced by printing no color where white is desired, and when fine white lines are required, a printing press must have printing stages exactly in register so that successive imprinting of differently colored dyes do not print in the fine white line area. Further, certain shading effects in which lighter and darker shades of the same color are sought can be difficult to obtain for some patterns.
These disadvantages are overcome by the present invention which utilizes a blocking agent capable of chemically reacting with the heat transfer dyes thereby binding the same to the substrate. The dye thus immobilized cannot be heat transferred to the article to be printed. By the use of such blocking agents, complicated patterns and designs can be economically and efficiently produced in which the transfer of the dye is partially or completely blocked thereby allowing lighter shades or no color to be produced over darker shades. It also allows for greater utilization of printing cylinders because from a given set of cylinders, a series of positive prints and a series of negative prints can be made without making additional engravings.
British Pat. No. 1,391,012 describes the use of a physical barrier layer consisting of a proteinaceous coating. While a physical barrier is capable of preventing sublimed dye from passing there through, the effectiveness of the barrier is dependent on the density and the heat stability of the barrier. Moreover, it must overlie the dye.
The blocking agent of the present invention is effective when deposited underneath as well as above the dye as it not only acts as a physical barrier but functions to chemically react with the dye and this will, to an extent, bind dye lying immediately above it. Further, in accordance with the present invention, heat transfer dyes can be selected so that one is reactive with the blocking agent while a second is non-reactive. This allows for a continuous overcoating of blocking agent which is capable of selectively allowing a dye to pass there through. Still further, the present invention is heat stable as its chemical reactivity is increased with heat.
A still further feature of the present invention is that a blocking agent can be incorporated in an ink which contains a dye with which it is non-reactive. This ink is then deposited over an ink containing a dye which is reactive with the blocking agent. As a result, the dye incorporated in the blocking agent is transferred but the dye below the blocking agent is blocked.